Magnetic beads have become a popular means of performing affinity separations and bioprocessing reactions. The beads can be pulled from suspension by applying a permanent magnet to the side of a vessel containing them. Many of the current protocols are not automated and still require the manual addition of reagents, collection, and resuspension of the beads. Automation usually involves the use of large electromagnets, which can be placed at the side of a tube or capillary to collect the beads and subsequently turned off so to release the beads. However, the currents typically required preclude their use in battery powered devices. Added engineering is also typically needed to make sure the heat generated by the coils does not interfere with the chemistry of the beads. These prior designs also do not provide any mixing of the beads with the solution while they are trapped. Certain prior designs also cause undesired aggregation of magnetic beads and/or fail to release the beads concentrated into a reduced volume as desired.
A need exists for a mechanically simple means of capturing magnetic beads from a flowing stream, providing some degree of mixing with the passing fluid, and releasing the beads back into the stream while minimizing aggregation.